The invention relates in general to a lifting device with a load wheel with a load chain and a hand chain wheel with a hand chain, and more particularly to a lifting device wherein the hand chain wheel is covered with a cover which is supported for rotation about the hand chain wheel and has chain guide openings.
U.S. Pat. No. 3,030,076 discloses a lifting device in form of a hoist or pulley block with a separately guided load and a hand chain, wherein the hand chain wheel is covered with a one-piece hand chain wheel housing which surrounds the hand chain wheel. That hand chain wheel housing is supported for rotation about the hand chain wheel and has chain guide openings for feeding and withdrawing the hand chain.
The rotatable arrangement of the hand chain wheel housing is intended to enable the chain guide openings to follow the pulling forces that act on the hand chain, so that the chain guide openings are approximately perpendicular to the pulling direction. The hand chain has then sufficient clearance for passing through the chain guide openings without friction. This arrangement advantageously reduces the friction losses and the pulling forces required for lifting a load.
However, the design of this lifting device, in particular of the cover for the hand chain wheel, is relatively complex. In practice, the chain can jam or jump in spite of the fact that the hand chain wheel housing is able to rotate. This causes the hand chain wheel to jerk or slip and thereby also bangs in the hand chain and the load chain. Moreover, during operation of the hand chain wheel in certain applications, the chain can produce annoying noise.
It would therefore be desirable to improve the design and functionality of a lifting device with a rotatably supported cover for the hand chain wheel.
According to one aspect of the invention, the cover is rotatably supported by a supporting metal sheet which is attached to a side plate of a housing that receives the load chain wheel. An outwardly oriented guide disposed on the cover engages with a slide ring on the supporting metal sheet. The slide ring has a central recess for the cover.
The guide on the cover is preferably formed as a circumferential collar, which can be formed by an S-shaped edge of the cover edge .
According to another embodiment of the invention, the guide can be formed by an edge seam of the cover edge facing the side plate.
The lifting device according to the invention is characterized by a functional cover for covering the hand chain wheel, wherein the cover is simple and reliably supported for rotation. The cover can be rotated by 360xc2x0 about the hand chain wheel and follows the pulling forces that act on the hand chain, so that the hand chain is always oriented along the pulling direction. The cover adjusts automatically according to the pulling direction of the hand chain. The lifting device of the invention can be operated from all directions, and the hand chain is no longer deflected on the chain guide openings. The hand chain can run smoothly and with only small friction losses perpendicular through the chain guide openings. The applied pulling force is thereby transferred to the hand chain wheel via the hand chain with low losses.
Advantageously, the cover can also be assembled in a simple manner. The hand chain wheel can be covered using only a few lightweight components. The cover together with the supporting metal sheet is adjusted and secured on the side plate of the housing, preferably with screws.
According to yet another embodiment of the invention, the slide ring is formed by an annular stamped portion of the supporting metal sheet, making fabrication of the device simple and economical.
According to yet another embodiment of the invention, the passage of the hand chain through the chain guide opening can be supported by sliding blocks associated with the chain guide openings. In a particularly preferred embodiment of the lifting device of the invention, the sliding blocks are made of plastic and form a part of a one-piece shell body incorporated in the cover. The shell body is preferably made of polyamide.
The shell body is placed in the cover and installed together with the cover. The shell body moves with the cover when the cover rotates. The sliding blocks reliably guide the hand chain through the chain guide openings. In addition, the sliding blocks also reduce noise. The rattling noise frequently observed during operation of the hand chain is strongly attenuated.
According to still another advantageous embodiment, one end face of the cover has an opening which is closed with a cover plate that is coupled with the hand chain wheel. The cover plate rotates with the hand chain wheel. The hand chain wheel and the load wheel are mounted on the drive shaft, wherein the end of the drive shaft facing the hand chain wheel is accessible via the cover plate.
Further features and advantages of the present invention will be apparent from the following description of preferred embodiments and from the claims.